In 2025, multiple outbreaks of Koi herpesvirus (KHV) disease have been confirmed in England and Wales, prompting immediate statutory controls by the Fish Health Inspectorate (FHI). KHV is a serious viral disease affecting all carp species, including ornamental koi, and can cause mass mortalities. The blog explains symptoms, legal obligations, confirmed designation restrictions, and control measures now in place to prevent further spread.
Koi Herpesvirus Disease Outbreaks Confirmed in England and Wales
The Fish Health Inspectorate (FHI) has confirmed new outbreaks of Koi herpesvirus (KHV) disease at multiple sites across England and Wales in 2025. This development has triggered immediate statutory controls and biosecurity measures in a bid to contain the spread of this highly contagious viral infection among carp populations.
KHV is a serious disease that affects all varieties of common and ornamental carp species (Cyprinus carpio), including the popular koi carp. It has the potential to cause mass mortalities in both commercial and hobbyist fisheries, making it a disease of major concern in the aquaculture and ornamental fishkeeping industries.
Symptoms and Risk Conditions
Infected fish often display visible signs of illness, particularly when water temperatures range between 16°C and 28°C. The most common symptoms of Koi Herpesvirus include:
- Necrotic (white or brown) patches on the gills
- Rough skin with sloughing mucous
- Sunken eyes
Anyone observing such symptoms in carp or carp hybrids is urged to contact the FHI without delay. Suspicion of an outbreak, especially in the presence of unexplained deaths, must also be reported immediately. While the disease poses no risk to human health, its impact on fish populations can be devastating.
Legal and Monitoring Requirements
Koi Herpesvirus is classified as a listed disease under The Aquatic Animal Health (England and Wales) Regulations 2009. The UK has maintained a formal surveillance programme for KHV since 2007, and statutory control measures are put in place immediately upon laboratory confirmation of the virus.
Once a site is confirmed as having a Koi Herpesvirus outbreak, it is placed under a Confirmed Designation. This triggers several legal restrictions and obligations for fishery operators and site managers:
- Movement of any aquatic animals, including eggs and gametes, into, out of, or within the confirmed designation area is prohibited without written consent from the FHI.
- Dead aquatic animals, eggs, and gametes must be disposed of using an approved method in accordance with local Environmental Health department requirements for Category 2 animal-by-product waste.
- Any reoccurrence of fish mortalities or spread to other water bodies within the designated area must be immediately reported to the FHI.
- All physical site changes such as modifications to boundaries, number or size of water bodies, or changes in site usage must be notified in advance. Written permission from the FHI is mandatory before implementing such changes.
- All consent requests required under a Confirmed Designation must be submitted to the FHI with at least five working days’ notice.
Control Measures and Biosecurity
When outbreaks are confirmed, the FHI applies rigorous disease control measures which may include:
- Enhanced biosecurity protocols
- Culling of infected fish
- Thorough cleaning and disinfection of affected premises
- Strict movement controls on all susceptible species
These steps are aimed at limiting the spread of Koi Herpesvirus and, where possible, completely eradicating the disease from infected sites. Fisheries and aquaculture sites are required to comply fully with all conditions laid down in the statutory notices to avoid further transmission.
Continuous Surveillance and Industry Responsibility
The ongoing surveillance programme for KHV in the UK plays a critical role in early detection and disease containment. The responsibility for disease management is shared between government agencies and private operators. Vigilance by fishery managers, ornamental fish keepers, and the general public remains essential in controlling the spread of Koi Herpesvirus.
With the 2025 outbreaks highlighting the persistent risk of this disease, all stakeholders in the aquatic sector are reminded to maintain high standards of biosecurity, report any signs of infection promptly, and adhere strictly to FHI guidelines.
These outbreaks are a stark reminder of the fragility of aquatic ecosystems and the importance of proactive disease monitoring and control in protecting the health of fish populations across the UK.
Disclaimer:
This blog is for informational purposes only and is based on publicly available updates from the Fish Health Inspectorate (FHI) regarding Koi herpesvirus (KHV) outbreaks in 2025. Readers are advised to contact the FHI or relevant authorities directly for the most accurate, up-to-date guidance and for reporting suspected cases. The information provided does not substitute official veterinary or regulatory advice.